Optimize Perl
By Martin C. Brown2005-04-11
Use AutoLoader
|
|
One of the most expensive portions of the execution of a Perl script is the compilation of source code into the bytecode that is actually executed. On a small script with no external modules, the process takes milliseconds. But start to include a few of your own external modules and the time increases. The reason is that Perl does little more with a module than importing the text and running it through the same compilation stage. That can turn your 200 line script into a 10,000 or 20,000 line script very quickly. The result is that you increase the initial stages of the compilation process before the script even starts to do any work.
During the normal execution of your script, it may be that you only use 10 percent, or even 5 percent, of all the functions defined in those modules. So why load them all when you start the script? The solution is to use AutoLoader, which acts a bit like a dynamic loader for Perl modules. This uses files generated by the AutoSplit system, which divides up a module into the individual functions. When you load the module through use, all you do is load the stub code for the module. It's only when you call a function contained within the module that the AutoLoader steps in and then loads and compiles the code only for that function. The result is that you convert that 20,000 line script with modules back into a 200-line script, speeding up the initial loading and compilation stages.
I've saved as much as two seconds just by converting one of my applications to use the AutoLoader system in place of preloading. It's easy to use by just changing your modules from the format shown in Listing 8 to that shown in Listing 9, and then making sure to use AutoSplit to create the loading functions you need. Note that you don't need to use Exporter any more; AutoLoader handles the loading of individual functions automatically without you have to explicitly list them.
Listing 8. A standard module
package MyModule;Listing 9. An autoloading module
use OtherModule;
require 'Exporter';
@EXPORT = qw/MySub/;
sub MySub
{
...
}
1;
package MyModule;The main difference here is that functions you want to autoload are no longer defined within the module's package space but in the data section at the end of the module (after the __END__ token). AutoSplit will place any functions defined here into the special AutoLoader files. To split up the module, use the following command line:
use OtherModule;
use AutoLoader 'AUTOLOAD';
1;
__END__
sub MySub
{
...
}
perl -e 'use AutoSplit; autosplit($ARGV[0], $ARGV[1], 0, 1, 1)' MyModule.pm auto
Tutorial Pages:
» Squeeze the Most From Your Code
» Sloppy Programming, Sloppy Performance
» Approaching Optimization
» Use References
» String Handling
» Loops
» Sorts
» Using Short Circuit Logic
» Use AutoLoader
» Using Bytecode and the Compiler Back Ends
» Other Tools
» Putting it All Together
» Resources
First published by IBM DeveloperWorks
|
| Related Tutorials: » Random subroutines in Perl » Log Script Use » Creating Perl Modules for Web Sites » Bit Vector, Using Perl Vec » Build a Perl/CGI Voting System » Perl Range Operator |